1. Field of the Invention
This invention relates to an infrared objective system lens for the wavelength range of 3.5 .mu.m-5 .mu.m.
2. Description of the Prior Art
Known infrared objectives of the above kind (e.g. DE-A-3008343) have either large chromatic aberrations or if not, their cost is rather high because of the required material. An achromatic infrared objective of low price and tolerable correction of monochromatic aberrations is desirable in particular for use with detectors of low resolution.